The invention is directed to industrial manipulators. More particularly, the invention is directed to a wrist for use in industrial manipulators. The improved wrist of this invention provides three degrees of freedom.
The introduction of robotics into the manufacturing facility has resulted in a demand for a variety of robotic components, such as end effectors which are gripper like devices which manipulate tools or components in the manufacturing process and wrists which can offer any number of degrees of freedom or levels of compliance. The specific application of the end effector to a given manufacturing process can require a multi-jointed, complex wrist design which provides several degrees of freedom. The dexterity of the end effector and the industrial manipulator is reflected in directional movement capabilities which are indicated as degrees of freedom.
It is an objective in the design and construction of industrial manipulators to mimic limited aspects of various human capabilities in order to improve the positional accuracy of industrial manipulators in a variety of tasks. A robot must be able to reach workpieces and tools. This requires a combination of an arm and a wrist subassembly, plus an end effector. The robot's sphere of influence is based upon the volume into which the robot's arm can deliver the wrist subassembly. A variety of geometric configurations have been studied and tried and their relative kinematic capabilities appraised. Such configurations include cartesian coordinates, cylindrical coordinates, polar coordinates and revolute coordinates. Evidently each of these configurations offers a different shape to its sphere of influence, the total volume of which depends upon arm link lengths. For different applications, different configurations may be appropriate. For example, a revolute arm might be best for reaching into a tub, while a cylindrical arm might be best suited to a straight thrust between the dies of a punch press.
In every case however, the arm carries a wrist assembly to orient its end effector as demanded by workpiece placement. Commonly, the wrist provides three articulations that offer motions labeled pitch, yaw and roll.
It should be noted that any of the arm coordinate systems requires three articulations to deliver the wrist assembly anywhere in this sphere of influence. It then requires three more articulations in the wrist for universal orientation of the end effector.
Quite often, robots are able to cope with job assignments without employing a full set of six articulations. This arises out of some symmetry in either the workpiece or the workpiece layout. For example, to move a bowling ball around in the sphere of influence requires only three articulations, because a ball is always oriented, irrespective of a gripper's orientation. More frequently, parts have one axis of symmetry, i.e. cylindrical, and this allows the robot arm to degenerate to five articulations.
Actually, five articulations are quite often adequate when the workpiece is arranged to reduce part manipulation needs. This happens, for example, when the beds of machine tools are all located parallel to one axis of a cartesian coordinate robot or on a radius of base rotation for cylindrical, polar or revolute robot arms. It may be argued that this compromising of the number of articulations is begging the question of robots versus special purpose automation. The rotor should be the universal solution, readily transferred to other applications. In this vein, reference should be made to the elegance of computer control of robot arms. Given a six articulation arm of any configuration, software can permit a program to be generated in cartesian coordinates irrespective of the choice of articulations. Indeed, the software can be powerful enough to think only in tool coordinates. That is, the programmer concerns himself with the tool on the end of the robot arm. He can think in terms of the tool's frame of reference and computer subroutines automatically make the various articulations move so as to accomplish the desired tool manipulation.
It is therefore an object of this invention to provide a hand gear train for use with an industrial manipulator. It is a further object of this invention to provide a hand gear train that provides more accurate positioning with three degrees of freedom.
It is yet another object of this invention to provide a hand gear train with three degrees of freedom which is readily adaptable to existing robots and robotic systems. It is still another object of this invention to provide a hand gear train which utilizes unique bearing placement and simplified bearing construction to provide a dimensionally smaller hand gear train which can be both easily upscaled and downscaled.